Field of the Invention
The present invention relates to a laser processing method for dividing a plate-shaped workpiece such as a wafer into chips by applying a laser beam having an absorption wavelength to the plate-shaped workpiece.
Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines are formed on the front side of a substantially disk-shaped semiconductor wafer to thereby define a plurality of separate regions, and a plurality of devices such as ICs and LSIs are formed in the respective separate regions. The semiconductor wafer is cut along the division lines to thereby produce a plurality of individual device chips, which are widely used in various electronic equipment such as mobile phones and personal computers.
Further, also in the case of an optical device wafer having a substrate such as a sapphire substrate and a silicon carbide substrate and a gallium nitride compound semiconductor layer formed on the front side of the substrate, the optical device wafer is cut along the division lines to obtain individual optical device chips such as light emitting diodes (LEDs) and laser diodes (LDs), which are used in various electrical equipment such as illumination equipment, backlight of LCD, and signal light.
As a method of dividing a wafer along the division lines, there has been proposed a method including the steps of applying a pulsed laser beam having an absorption wavelength to the wafer along each division line to thereby form a laser processed groove as a break start point along each division line, and next applying an external force to the wafer along each division line where the laser processed groove is formed, thereby breaking the wafer along each division line (see Japanese Patent Laid-open Nos. 2004-188475 and 2007-019252, for example). In applying the pulsed laser beam having an absorption wavelength to the wafer along each division line, the wafer is preliminarily attached to an adhesive tape supported to an annular frame, wherein the adhesive tape is composed of a base film of polyvinyl chloride and an adhesive layer of acrylic resin formed on the front side of the base film, so as to keep the divided individual device chips in position.